Illnesses associated with higher elevation are one of the major hazards of this sport. Research has shown that blood clotting changes with higher altitudes. Furthermore, people with high altitude illness have evidence of excessive blood clotting. Unfortunately, much of this research was done before many modern tests of coagulation were devised. In addition, intense exercise also affects blood coagulation and this was not controlled for in these earlier efforts. The purpose of this project will be to systemically study the effects of high altitudes (specifically hypoxia [low oxygen levels]) with and without exercise on blood coagulation. This project will control for the effects of exercise and use modern laboratory techniques to assay coagulation changes. We will store participants' blood for at the most six months until ten subjects have been enrolled and the results will be assayed at that time. This study requires participation on three separate days in the Clinical Research Center at OHSU. These days need not be consecutive but can be arranged at the partipant's convenience.